Currently, in a communication system, a wired network and a wireless network are mixed. FIG. 1 is a diagram illustrating an example of a communication system. A wireless local area network (LAN) terminal performs, for example, packet communication with a communicating party through a wireless link between the wireless LAN terminal and a wireless LAN base station (that is, access point: AP) and through a wired link between the wireless LAN base station and the communicating party (see FIG. 1). The wired link is, for example, the Ethernet (registered trademark).
In addition, as illustrated in FIG. 1, in the communication system, there exists a relay device. The relay device is connected to the wireless LAN base station through the wireless link, and connected to a relay destination device through the wired link. That is, the relay device connects the wireless LAN and the wired LAN.
Here, an allowable range of a payload length in the Ethernet® (hereinafter simply referred to as an “allowable range”) is 46 to 1500 bytes. FIG. 2 is a diagram illustrating a format of a MAC frame in the Ethernet®. The payload length is a length of a portion except for a media access control (MAC) header. On the other hand, the maximum value of the allowable range in 802.11b/a/g of the Institute of Electrical and Electronics Engineers, Inc. (IEEE) that is standard of a wireless LAN is 2304 bytes. That is, in the communication system, networks having different allowable ranges are mixed.
In order to avoid inconvenience due to such mixed networks having different allowable ranges in the communication system, a packet having a payload length that corresponds to the smallest allowable range in the plurality of allowable ranges is transmitted. That is, in the wireless LAN of the communication system, a MAC service data unit (SDU) is configured by the payload length of the allowable range of the Ethernet®, and a MAC frame of the wireless LAN is configured in units of the MAC SDU. FIG. 3 is a diagram used to explain a relationship between a configuration of a MAC frame in a wired LAN and a configuration of a MAC frame in a wireless LAN.
In addition, in IEEE802.11n that is current standard of a wireless LAN, a scheme that is called “aggregation” has been introduced. In such a scheme, an aggregation MAC SDU is formed by aggregating a plurality of MAC SDU, and the formed aggregation MAC SDU is transmitted by a single MAC frame. FIG. 4 is a diagram used to explain such aggregation. By using such aggregation, transmission efficiency of the wireless LAN may be improved as compared with IEEE802.11b/a/g. Here, the maximum value of an “allowable range” corresponds to the maximum length of a MAC SDU.
Japanese Laid-open Patent Publication No. 2003-324445 and Japanese Laid-open Patent Publication No. 2005-184839 are examples of the related art.